CP - Transport Across Cell Membranes

Question 1

What is non-mediated transport?

Answer 1

Transport that doesn’t directly use a transport protein

Question 2

What is mediated transport?

Answer 2

Move materials with the help of transport proteins

Question 3

What is passive transport?

Answer 3

Moves substances down their conc. or electrochemical gradients with only their kinetic energy

Question 4

What is active transport?

Answer 4

Uses energy to drive substances against their conc. or electrochemical gradients

Question 5

What is vesicular transport?

Answer 5

Moves materials across membranes in small vesicles either by exocytosis or endocytosis

Question 6

What type of diffusion is non-mediated transport and why?

Answer 6

Passive diffusion, because there is no transport protein to make molecules go against diffusion laws so conc. gradient is higher outside the cell than inside

Question 7

What is non-mediated diffusion important for?

Answer 7

Absorption of nutrients and excretion of wastes

Question 8

What types of molecules is transported by non-mediated transport?

Answer 8

Non-polar, hydrophobic molecules, e.g. O2, CO2, N2, fatty acids, steriods, small alcohols, NH3, fat-soluble vitamins (A, D, E, K)

Question 9

What are ion channels?

Answer 9

Water filled pores that span the hydrophobic core of the lipid bilayer and allow passage of ions (and small molecules) across the cell membrane

Question 10

What do ions not bind to?

Answer 10

Channel pore, so transport is very rapid

Question 11

What is the water filled pore lined by?

Answer 11

Hydrophilic amino acids (i think it might be hydrophobic? - perla)

Question 12

What determines the ionic selectivity of ion channels?

Answer 12

Specific amino acids lining the pore

Question 13

By being selective to particular ion, the channel can?

Answer 13

Harness the energy stored in the different ion gradients

Question 14

What can discriminate ions based on their size and the amount of water they have around them?

Answer 14

Shape of selectivity filter

Question 15

What do channels contain to control the opening and closing of the pore?

Answer 15

Gates

Question 16

What can control the (gate) channel from opening and closing?

Answer 16

Different stimulis, e.g. Voltage, Ligand binding, Cell volume (stretch), pH and Phosphorylation

Question 17

How can we measure ion channel function/the current flowing through an individual channel?

Answer 17

Patch clamp technique

Question 18

What do current fluctuations represent?

Answer 18

Opening and closing of single ion channels and the changes in channel structure that are associated with channel gating

Question 19

The diffusion of ions through a channel generates a measurable current across the membrane of how much?

Answer 19

10^-12 amps (dont need to know) - perla

Question 20

What types of transport can carrier mediated transport be?

Answer 20

Passive (faciliated) or active

Question 21

What is carrier mediated transport?

Answer 21

The substrate to be transported directly interacts with the transporter protein

Question 22

Why are transport rates slower for carrier mediated transport than those obtained for channels?

Answer 22

Transporter undergoes a conformational change

Question 23

Carrier transport proteins have similar properties to ___

Answer 23

enzymes

Question 24

What do transport proteins do? (+ do they catalyze chemical reactions?)

Answer 24

They mediated transport across the cell membrane at a faster rate than normal (they don’t catalyze chemical reactions)

Question 25

What do carriers exhibit?

Answer 25

Specificity; Inhibition; Competition; Saturation (transport max.)

Question 26

What do transporters display?

Answer 26

Enzyme kinetics

Question 27

When does glucose transport occur until?

Answer 27

All binding sites are saturated

Question 28

What is the term to describe passive mediated transport?

Answer 28

Facilitated diffusion

Question 29

What happens in facilitated diffusion of glucose (3 steps)?

Answer 29

1. Glucose binds to a transport protein (GLUT)
2. Transport protein changes shape and glucose moves across cell membrane (diffusing down its conc. gradient)
3. Kinase enzyme reduces glucose conc. inside the cell by converting glucose into glucose-6-phosphate. This conversion of glucose maintains the conc. gradient for continued glucose absorption

Question 30

What is primary active transport?

Answer 30

Energy is directly derived from hydrolysis of ATP

Question 31

How much % of a typical cell’s energy (ATP) does it use on primary active transport?

Answer 31

30% dont need to know this - perla

Question 32

What is secondary active transport?

Answer 32

Energy stored in an ionic conc. gradient is used to drive the active transport of a molecule against its gradient
OR
Energy released by a substance diffusing down its conc. gradient is used to actively transport another substance against its conc. gradient

Question 33

What type of active transporter is the Na/K ATPase pump?

Answer 33

Primary active transporter

Question 34

What does the Na/K ATPase pump maintain?

Answer 34

Low conc. of Na+ and high conc. of K+ in the cytosol

Question 35

How does the Na/K ATPase pump work (4 steps)?

Answer 35

1. Na+ binds to the binding pocket
2. The binding causes ATP to convert to ADP and a phosphate group attaches to the pump, causing it to change its shape. Na+ is removed.
3. K+ binds and phosphate group detaches
4. The release of phosphate group reverts pump back to its original form and K+ is pumped into the cell

Question 36

How many Na+ ions are removed and how many K+ ions are pumped into the cell?

Answer 36

3 Na+ ions and 2 K+ ions (don’t need to know)

Question 37

What does the Na/K ATPase pump generate?

Answer 37

A net current and is electrogenic

Question 38

What is the difference in ion conc. important for?

Answer 38

• Maintain resting membrane potential
• Electrical excitability
• Contraction of muscle
• Mainteinance of steady state volume
• Uptake of nutrients via secondary active transport
• Mainteinance of intracellular pH by secondary active transporters

Question 39

What is the pump-leak hypothesis?

Answer 39

The pump works continuously due to the continual leakage of Na+ ions into the cell and K+ ions out of the cell (down their respective gradients)

Question 40

What are other examples of primary active transport?

Answer 40

Ca2+/K+ ATPase (in muscle cells) and H+/K+ ATPase (in stomach)

Question 41

What is secondary active transport?

Answer 41

Uses the energy stored in an ion gradient created by primary active transporters to move other substances against their own conc. gradient (indirectly use the energy obtained by hydrolysis of ATP)

Question 42

Cells have many secondary active transporters which are powered by what gradient?

Answer 42

Na+ gradient, initially established by the Na/K pump

Question 43

What occurs in Na+ antiporters or exchangers?

Answer 43

When Ca2+ or H+ binds to the protein, Na+ ions rush inward (down its electrochemical gradient) and Ca2+ or H+ ions pushed out

Question 44

What occurs in Na+ symporters or cotransporters?

Answer 44

When glucose or amino acids binds to the protein, it opens the channel, so that Na+ ions diffuse down its electrochemical gradient, together with glucose or amino acids rushing inwards (against their conc. gradients)